Naturally Abundant Green Moss for Highly Efficient Solar Thermal Generation of Clean Water

Universal Comparison of Interfacial Solar-Assisted Evaporation Systems

Interfacial solar-assisted evaporation (ISAE) systems are among the promising technologies for the preparation of drinkable water because they utilize renewable energy (sunlight energy), which is abundant and available in most countries. To compare and select the best ISAE systems, uniform (universal) parameters must be used. Herein, two parameters, evaporation rate (without a theoretical limit) and solar-to-vapor conversion efficiency (having a theoretical limit), were introduced for the universal comparison of ISAE systems.

Advancing Efficiency in Solar-Driven Interfacial Evaporation: Strategies and Applications

Solar-driven interfacial evaporation (SDIE) has emerged as a promising technology for addressing global water scarcity by utilizing solar-thermal conversion and evaporation at the air/material/water interface. The exceptional performance of these systems has attracted significant interest; it is imperative to establish rigorous and scientific standards for evaluating effectiveness, optimizing system design, and ensuring efficient practical applications. In this Review, we propose consensus criteria for accurately assessing system performance and guiding future advancements. We then explore the fundamental mechanisms driving system synergy, emphasizing how material compositions, microscopic hierarchical material structures, and macroscopic three-dimensional spatial architecture designs enhance solar absorption and photothermal conversion; balance heat confinement with water pathway optimization; manage salt resistance; and regulate enthalpy during vaporization. These matched coordination strategies are crucial for maximizing the target SDIE efficiency. Additionally, we investigate the practical applications of SDIE technologies, focusing on cutting-edge progress and versatile water purification, combined with atmospheric water harvesting, salt collection, electric generation, and photothermal deicing. Finally, we highlight the challenges and exciting opportunities for advancing research, emphasizing future efforts to integrate fundamental principles, system-level collaboration, and application-driven approaches to boost sustainable and highly efficient water and energy technologies. By linking system performance evaluation with optimization strategies for influencing factors, we offer a comprehensive overview of the field and a future outlook that promotes highly efficient clean water production and synergistic applications.

Considering Micro/nanostructures at the Surface of Photothermal Materials: A Game Changer in Correct Estimation of Evaporation Rate and Energy Conversion Efficiency in Interfacial Solar Vapor Generation Systems

Interfacial solar evaporator generation (ISVG) is a new, cost-effective, and eco-friendly emerging method for water desalination. Two main criteria for evaluating ISVG performance are evaporation rate (ṁ) and solar-to-vapor conversion efficiency (η). The main challenge of the previously presented models for the estimation of ṁ and η in 2D systems is that in most cases the calculated values are beyond the theoretical limits, ṁ > 1.47 kg m-2 h-1 and η > 100%, both of which are not acceptable from the thermodynamics viewpoint. Also, the recently presented strategy of reduced vaporization enthalpy for obtaining η < 100% is unacceptable from the thermodynamics approach for ISVG as a two-step continuous process. Therefore, this work aims to present a model and consequently new equations for the correct estimation of evaporation rate and energy conversion efficiency in two-dimensional (2D)-ISVG systems, which are consistent with their corresponding theoretical limits. The basis of the present model is discrimination between the projection area and evaporation area by considering the micro/nanostructures on the surface of interfacial support (photothermal material). This leads to the presentation of new equations for ṁ and η having consistency with thermodynamics laws. The presence of micro/nanostructures on the surface of photothermal material provides a higher evaporation area which is not considered in the previous models and led to theoretically inconsistent results. The results of the present study provide a theoretical basis for the correct estimation of the evaporation rate and energy conversion efficiency in 2D-ISVG systems in future works.

Welding Pollen-Based Solar Evaporator for Clean Water Production

The world faces a trade-off between water availability and food supply, as agricultural irrigation consumes the largest freshwater globally. Inspired by inherent water transport channels in plants, a cost-effective welding pollen-based solar evaporator (PSE) is developed to obtain clean water from seawater desalination. Based on the convex and folded surface structure of natural pollen (Helianthus annuus) and the porous structure of welding pollen evaporator interconnection, the PSE reveals an efficient evaporation rate of 1.86 kg m-2 h-1 under one-sun illumination and further exhibits excellent cycling performance for 10 cycles tested in 7.0 wt.% saline water without salt accumulation. In addition, PSE has superior mechanical stability (3.44 MPa) and remains stable after being immersed in pH 1 and 14 solutions for 24 h without sacrificing mechanical properties. Importantly, the work has demonstrated the success of the freshwater collected from the evaporation process, which can effectively facilitate the cultivation of lettuce, rice, and wheat. These findings highlight the practical application of pollen as a low-cost, eco-friendly natural resource in interfacial solar evaporation. Furthermore, they inspire addressing current global water scarcity and promoting sustainable agriculture.

Cost Effective Photothermal Materials Selection for Direct Solar-Driven Evaporation

The cornerstone of eco-friendly and affordable freshwater generation lies in harnessing solar energy for water evaporation. This process involves extracting vapor from liquid water using solar energy. Numerous innovative, low-cost materials have been proposed for this purpose. These materials aim to enable highly controllable and efficient conversion of solar energy into thermal energy while maintaining high cost-effectiveness. Here, in this review paper, we outline the advancements in solar-driven evaporation technology with a focus on optimizing synthesis methods and materials cost. It prioritizes refining evaporation efficiency and affordability using inventive manufacturing methods. By utilizing innovative reasonably priced materials, this process not only ensures efficient resource utilization but also fosters technological advancements in renewable energy applications. Moreover, the affordability of these materials makes solar-powered water evaporation accessible to a wider range of communities, empowering them to address water scarcity challenges.

Water Activation in Solar-Powered Vapor Generation

Solar-powered vapor evaporation (SVG), based on the liquid-gas phase conversion concept using solar energy, has been given close attention as a promising technology to address the global water shortage. At molecular level, water molecules escaping from liquid water should overcome the attraction of the molecules on the liquid surface layer to evaporate. For this reason, it is better to reduce the energy required for evaporation by breaking a smaller number of hydrogen bonds or forming weak hydrogen bonds to ensure efficient and convenient vapor production. Many novel evaporator materials and effective water activation strategies have been proposed to stimulate rapid steam production and surpass the theoretical thermal limit. However, an in-depth understanding of the phase/enthalpy change process of water evaporation is unclear. In this review, a summary of theoretical analyses of vaporization enthalpy, general calculations, and characterization methods is provided. Various water activation mechanisms are also outlined to reduce evaporation enthalpy in evaporators. Moreover, unsolved issues associated with water activation are critically discussed to provide a direction for future research. Meanwhile, significant pioneering developments made in SVG are highlighted, hoping to provide a relatively entire chain for more scholars who are just stepping into this field.

Stable polyethylene glycol/biochar composite as a cost-effective photothermal absorber for 24 hours of steam and electricity cogeneration

Seawater desalination powered by solar energy is the most environmentally and economical solution in responding to the global water and energy crisis. However, solar desalination has been negatively impacted by intermittent sun radiation that alternates between day and night. In this study, sugarcane bagasse (SCB) was recycled via the pyrolysis process to biochar as a cost-effective solar absorber. Besides, polyethylene glycol (PEG) as a phase change material was encapsulated in the abundant pore structure of biochar to store the thermal energy for 24 hours of continuous steam generation. The BDB/1.5 PEG evaporator exhibited an evaporation rate of 2.11 kg m-2 h-1 (98.1% efficiency) under 1 sun irradiation. Additionally, the BDB/1.5 PEG evaporator incorporated by the TEC1-12706 module for continuous steam and electricity generation with a power density of 320.41 mW m-2. Moreover, 10 continuous hours of evaporation were applied to the composite demonstrating outstanding stability. The composite exhibited high water purification efficiency through solar desalination due to the abundant functional groups on the biochar surface. Finally, the resulting low-cost and highly efficient PCM-based absorber can be used on a wide scale to produce fresh water and energy.

Carbon nanofiber reinforced carbon aerogels for steam generation: Synergy of solar driven interface evaporation and side wall induced natural evaporation

Solar-based interface evaporation (SIE) is a green, efficient and cost-effective technique to harvest fresh water. 3D solar evaporators show their unique advantages in gaining energy from environment and hence possess a higher evaporation rate than 2D evaporators. However, much effort is still required to develop mechanically robust and superhydrophilic 3D evaporators with strong water transportation capability and salt-rejection performance, and at the same time reveal how they gain energy from environment via the natural evaporation. In this work, a novel carbon nanofiber reinforced carbon aerogel (CNFA) is prepared for the SIE. The CNFA has a high light absorption up to 97.2% and outstanding photothermal conversion performance. The heteroatom doping and hierarchically porous structure endow the CNFA with superhydrophilicity and thus powerful water transportation capability and salt rejection performance. Benefiting from synergy of the SIE and side wall induced natural evaporation, the CNFA evaporator exhibits a high evaporation rate and efficiency (as high as 3.82 kg m^-2h^-1 and 95.5%, respectively) with long-term stability and durability. The CNFA can also work normally in high-salinity and corrosive seawater. This study demonstrates a new method to fabricate all-carbon aerogel solar evaporators and provides insights for the effective thermal management during the interface evaporation.

Scalable, Green, and Cost-Effective Carbonized Sand for Efficient Solar Desalination

Nowadays, sweet and drinkable water shortage is a global issue which has attracted widespread attention. Desalination of seawater as the greatest source of water on our planet using solar energy as the most abundant and green energy source for producing fresh water can help us address this issue. Interfacial solar desalination is a state-of-the-art, sustainable, green, and energy-efficient method that has been studied lately. One of the key parameters for researching this method with reasonable efficiency is a photothermal material. Herein, carbon-coated sand was synthesized using abundant, green, and low-cost materials (sand and sugar), and its performance as a photothermal material is investigated and reported. In this work, a three-dimensional (3D) system is introduced to develop the performance and efficiency of the system under real sun irradiation and natural circumstances. The salt rejection ability of the system is another important thing we should notice due to the high salinity of seawater that we want to desalinate. The superhydrophilic carbonized sand demonstrated a good evaporation rate of 1.53 kg/m²h and 82% efficiency under 1 sun irradiation and upright salt rejection ability, which exhibited its capability to be used in green solar-driven water vaporization technology for sweet water production. The effects of important parameters, including light intensity, wind speed, and environment temperature, on the evaporation rate using carbonized sand as a solar collector in a solar desalination system were studied in both laboratory and real systems.

MXene/polypyrrole coated melamine-foam for efficient interfacial evaporation and photodegradation

The application of photothermal materials in seawater desalination, wastewater treatment have been widely studied, however, there are relatively few studies that combine photothermal effects and solar-driven photocatalysis and exhibit efficient solar-driven water evaporation performance and excellent photocatalytic ability. Form the perspective of practical application, it is of great significance to combine photothermal effect with solar-driven photocatalysis to develop environment-friendly evaporator with low cost, simple preparation process and ability of seawater desalination, wastewater treatment and photodegradation of organic dyes. In this paper, a novel multifunctional MXene/polypyrrole (PPy) coated melamine foam (MF) named as MF-MXene/PPy was successfully prepared by simple impregnation and in-situ polymerization. The MF-MXene/PPy has rich porosity (89.13 %), abundant water molecule transport channels, excellent light absorption capacity (about 94 %), low thermal conductivity (0.1047 W m^-1 K^-1), and exhibits excellent performance in solar desalination, wastewater purification and photodegradation of organic dyes. Under 1 kW m^-2 illuminate, the solar energy conversion rate and efficiency of MF-MXene/PPy reaches up to 1.5174 kg m^-2h^-1 and 91.24 %. Moreover, due to the regular pore size of MF-MXene/PPy, good salinity tolerance was shown even after continuous evaporation in 20 wt% NaCl for 8 h. After continuous evaporation in 70 mL of 20 wt% NaCl for 8 h, the amount of salt collected could reach 0.2 g. In addition, MF-MXene/PPy also possessed excellent visible light degradation ability for organic dyes, and the degradation rate of methylene blue (MB), rhodamine B (RHB) and methyl orange (MO) were 92.38 %, 88.92 % and 91.75 %, respectively. As a fundamental research, this research will open a novel way to the development of new evaporator.

3D carbonized grooved straw with efficient evaporation and salt resistance for solar steam generation

Solar steam generation (SSG) is considered an effective solution to the global shortage of freshwater resources. To solve the practical application challenges of SSG in remote outdoor environments where electricity is scarce, it is of great importance to developing new solar evaporators. In this study, a three-dimensional (3D) biochar solar evaporator based on carbonized grooved straw was prepared from agricultural waste corn straw, which had high solar energy conversion efficiency and excellent salt resistance. The existence of grooves increases the surface area to absorb more sunlight and makes the light multilevel reflection improve the evaporation rate. The excellent light absorption, super hydrophilic, and heat shielding properties of 3D carbonized grooved straw resulted in a good evaporation rate (1.57 kg⋅m^-2·h^-1) and energy efficiency (85.9%) under 1 sun irradiation. The 3D grooved biochar solar distiller also demonstrated efficient formation evaporation performance and excellent salt resistance in practical applications in seawater desalination and surface water purification. The 3D grooved biochar solar distiller prepared from agricultural waste has the advantages of being economical and environmentally friendly, with good application prospects.

Water Harvesting Strategies through Solar Steam Generator Systems

Solar steam generator (SSG) systems have attracted increasing attention, owing to its simple manufacturing, material abundance, cost-effectiveness, and environmentally friendly freshwater production. This system relies on photothermic materials and water absorbing substrates for a clean continuous distillation process. To optimize this process, there are factors that are needed to be considered such as selection of solar absorber and water absorbent materials, followed by micro/macro-structural system design for efficient water evaporation, floating, and filtration capability. In this contribution, we highlight the general interfacial SSG concept, review and compare recent progresses of different SSG systems, as well as discuss important factors on performance optimization. Furthermore, unaddressed challenges such as SSG's cost to performance ratio, filtration of untreatable micropollutants/microorganisms, and the need of standardization testing will be discussed to further advance future SSG studies.

Reviewing wood-based solar-driven interfacial evaporators for desalination

Solar‒driven interfacial water evaporation is a convenient and efficient strategy for harvesting solar energy and desalinating seawater. However, the design and fabrication of solar evaporators still challenge reliable evaporation and practical applications. Wood-based solar-driven interfacial water evaporation emerge as a promising and environmentally friendly approach for water desalinating as it provides renewable and porous structures. In recent years, surface modifications and innovative structural designs to prepare high performance wood-based evaporators is widely explored. In this review, we firstly describe the superiority of wood for the fabrication of wood-based solar evaporators, including the pore structure, chemical structure and thermal insulation. Secondly, we summarize the recent developments in wood-based evaporators from surface carbonization, decoration with photothermal materials, bulk modification and structural design, and discuss from the aspects of water transportation capacity, thermal conductivity and photothermal efficiency. Finally, based on these previous results and analysis, we highlight the remaining challenges and potential future directions, including the selection of high-efficient photothermal materials, heat and mass transfer mechanism in wood-based evaporators including large-scale production at a low cost.

Three-Dimensional Artificial Transpiration Structure Based on 1T/2H-MoS2/Activated Carbon Fiber Cloth for Solar Steam Generation

The rise of solar steam generation is an effective strategy to mitigate clean water shortages. However, achieving further improvements in conversion efficiency and stability remains a challenge. Here, 1T/2H-MoS₂ nanosheets were uniformly assembled on activated carbon fiber cloth (A-CFC) through a facial hydrothermal method, and a three-dimensional (3D)-artificial transpiration device (ATD) was prepared using the plant transpiration process. The combination of activated carbon fiber cloth and 1T/2H phase MoS₂ exhibits high light absorption (∼97.5%), excellent mechanical stability, large evaporation area, and easy escape of vapor. Additionally, the 3D hollow cone of the MoS₂/carbon fiber cloth can effectively reduce radiative and convective energy loss and then achieve the enhancement of energy collection from the environment. An outstanding evaporation rate of 1.61 kg·m^-2·h^-1 with an optimum conversion efficiency of 97% under one sun is reached. Based on the facile fabrication, excellent stability, and high solar conversion efficiency, this nature-inspired design of 3D 1T/2H-MoS₂/A-CFC is expected to facilitate large-scale applications for seawater purification and desalination.

MXene-doped kapok fiber aerogels with oleophobicity for efficient interfacial solar steam generation

Although the evaporation efficiency of photothermal materials (PMs) in pure water and brine solutions has been extensively studied, there few research on the performance in complex oily wastewater. Herein, a new monolithic solar steam generator derived from kapok fiber-based MXene composite aerogel (named as KFs-MXene) was fabricated by dipping the aerogels (KFs) which composed of kapok fiber and sodium alginate (SA) as substrates in the suspension of MXene. Benefitting from the outstanding light absorption (about 97%), better thermal insulation (thermal conductivity, 0.05039 W m^-1 K^-1), abundant porosity (95.60%) and rapid water transportation. KFs-MXene show good interfacial solar steam generation (ISSG) performance, resulting in a high water evaporation rate of 1.47 kg m^-2h^-1 with an outstanding evaporation efficiency of 90.4% under 1 kW m^-2 irradiation. To improve the antifouling performance of KFs-MXene, chemically hydrophilic and oleophobic modification was applied, making the KFs-MXene can also be widely used in oily wastewater. Under 1 kW m^-2 illumination, the evaporation rate and energy conversion efficiency of KFs-MXene with hydrophilic and oleophobic modification (O-KFs-MXene) in 1 wt% oily water can reach to 1.40 kg m^-2h^-1 and 82.87%, and the evaporation efficiency and rate of O-KFs-MXene remain stable in the continuous 6 h solar driven interface evaporation process.

Solar distillation meets the real world: a review of solar stills purifying real wastewater and seawater

Solar energy-driven evaporation-based freshwater production is one of the sustainable ways to purify contaminated/salty water. Recent advances in solar absorbers' assemblies, design modifications, and integrations with heating sources improved the rate of freshwater productivity. However, the type of feed water affects the evaporation rate in a solar desalination system (SDS). Many studies used tap water with added contaminants to test the performance of a SDS and studied the water quality improvement. As a typical result, pH, total dissolved solids (TDS), and electrical conductivity (µS/cm) are reduced after solar evaporation. The performance of SDSs for real wastewaters are also important to understand, e.g., the reduction of high organic pollutants after solar evaporation. In this aspect, the main objective of the present work is to review solar distillation of real wastewaters and seawater by using SDSs. Further, the mechanism of a solar distiller with heat transfer principles, parameters affecting evaporation process, real wastewaters and seawaters purified in a solar distillation system, improvement of various parameters before and after solar evaporation, pathways of handling wastewaters, challenges, and future perspectives are discussed. Conclusively, SDSs are found to remove pollutants effectively after solar evaporation. The evaporation rate is relatively slower due to high concentration of pollutants that reduce vapor pressure. The COD removal of various real wastewaters, including sludge, kitchen, textile, palm oil, petroleum, water plant, and municipal wastewaters, was 98.13%, 97.85%, 96.84%, 96.71%, 87.99%, 86.99%, and 85.67%, respectively. The reduction rate of salt concentration in real seawater after evaporation in the solar distiller was 99.99%.

Hierarchically Designed Three-Dimensional Composite Structure on a Cellulose-Based Solar Steam Generator

The emerging water purification technology represented by solar water evaporation has developed rapidly in recent years and is widely used in seawater desalination. However, the high reflectivity of sunlight and low efficiency of photothermal conversion greatly hinder its application prospects. In this paper, the hierarchical structure of the film was designed and optimized by the addition of carbon materials in the process of bacterial cellulose culture. A cellulose-based composite film material with a microporous structure was obtained, which can improve the photothermal evaporation rate and photothermal conversion efficiency from the structural principle to improve the stability of floating on the water. Bacterial cellulose (BC) as a three-dimensional carrier was combined with one-dimensional and two-dimensional (1D/2D) compounds of carbon nanotubes (CNT) and reduced graphene oxide (RGO) to form composite films for solar evaporation. By the addition of CNT-RGO (21.8 wt %), the composite showed prominent photothermal evaporation rate and photothermal conversion efficiency properties. Through in situ culture of BC, not only a tight structure can be obtained but also the surface of BC contains a large number of hydroxyl groups, which have many active sites to load photothermal materials. BC nanofibers, CNT, and RGO cooperate to form a porous network structure, which provides continuous double channels for the rapid transmission of water molecules and light paths, so as to form an excellent photothermal layer. The photothermal conversion efficiency is 90.2%, and the photothermal evaporation rate is 1.85 kg m^-2 h^-1 to achieve efficient solar interface evaporation. This is a high level of photothermal properties in a cellulose-based solar steam generator. The superior photothermal performance of this hybrid film possesses scalability and desalination ability.